Magenis, Marilyn Alice, authorBrandl, Alexander, advisorJohnson, Thomas E., committee memberVolckens, John, committee memberHarton, John, committee member2007-01-032007-01-032013http://hdl.handle.net/10217/80267A new method for subtraction of extraneous cosmic ray background counts from liquid scintillation detection has been developed by Hidex™. The method uses a background counter located beneath the liquid scintillation detector, the guard, to account for background signals. A double to triple coincidence counting methodology is used to reduce photomultiplier noise and to quantify quench. It is important to characterize the interactions from background in any new system. Characterizing interactions in the instrument will help to verify the accuracy and efficiency of the guard by determining the noise cancellation capabilities of the liquid scintillation counter. The liquid scintillation counter and guard detector responses were modeled using MCNP for the expected cosmic ray interactions at the instrument location and altitude in Fort Collins, CO. Cosmic ray interactions in the detector are most relevant to examine because of their predominance due to the higher elevation in Fort Collins. The cosmic ray interactions that are most important come from electron, positron, and gamma interactions. The expected cosmic ray interactions from these particles were modeled by using a cosmic ray library that determines the cosmic rays that are most likely to occur at an altitude of 2100 meters. The model predictions were then compared to the instrument background measurements. The results suggest that the cosmic ray contribution to the instrument background is negligible.born digitalmasters thesesengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.Text